feat: add PNG decoder, query3/4, Capsule+GJK/EPA, friction, Lua engine API

- PNG decoder with self-contained Deflate decompressor (RGB/RGBA)
- ECS query3 and query4 for multi-component queries
- Capsule collider + GJK/EPA narrow phase for convex shapes
- Coulomb friction in physics solver
- Lua engine API bindings (spawn, position, entity_count)

Tests: 255 → 286 (+31)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -2152,6 +2152,8 @@ name = "voltex_script"
 version = "0.1.0"
 dependencies = [
  "cc",
+ "voltex_ecs",
+ "voltex_math",
 ]
 
 [[package]]